1. Field of the invention
The present disclosure relates to an organic light emitting display (“OLED”) device, and more particularly, to an active matrix OLED device and a method for driving the same.
2. Description of the Related Art
Recently, a display device that is lightweight, compact and requires low power consumption is in demand for use in mobile communications. An OLED device is a self-luminous device while generates light by itself, provides superior viewing angle and a contrast ratio relative to a liquid crystal display (“LCD”) device. In addition, since the OLED device does not require a backlight unit, it has the additional advantages of reduced weight, thickness, and power consumption.
The OLED device is classified into a passive matrix type and an active matrix type. In the passive matrix type OLED device, an anode and a cathode are formed to cross each other and the OLED device is driven by selection of a line. The active matrix type of OLED device controls a current flowing into an OLED element by maintaining a driving voltage switched by a switching transistor by a capacitor and applying the driving voltage to a driving transistor.
However, in a conventional active matrix OLED device, a characteristic of a threshold voltage of the driving transistor varies according to a location of an OLED panel. The variation of the threshold voltage is the result of a process error during fabricating a thin film transistor. Accordingly, even though the same driving voltage is applied to driving transistors of pixels, the current flowing into OLED elements may be different from each other. As a result, the respective pixels display images with different luminances. In other words, the variation of the threshold voltage of the driving transistor of the OLED panel appears as non-uniformity of the luminance and a spotted image.
When the variation of the threshold voltage of the driving transistor shows a different white level and a different black level in the OLED panel, characteristics of each OLED panel, such as a luminance and a contrast ratio, are not constant according to the OLED panel.